Crystal-field and Nd-Mn exchange interaction in Nd_2/3Ca_1/3MnO₃

Abstract

A study of the low field magnetization and specific heat in magnetic fields up to 9 T of Nd2/3Ca1/3MnO3 perovskite in the 2-30 K temperature range has been done. All the specific heat data show broadened Schottky-like anomaly below 20 K. We suppose that such a behavior originates from the Nd magnetic ordering caused by the splitting of the Nd3+ ions ground-state doublet (GSD) in the effective molecular field Hex of Mn spin system supplemented by an applied external magnetic field. The zero field GSD splitting is an evidence of a strong exchange coupling between Nd and Mn magnetic subsystems. The Nd-ions magnetic ordering introduces an additional contribution to the ferromagnetic moment producing anomalies of the field-cooled and zero-field-cooled magnetizations of the system below 28 K. The broadened Schottky-like anomalies found are fitted for every field by a set of three Schottky functions. Applied magnetic field extends the anomaly region and shifts it to the higher temperatures. Splitting of the higher crystal field Kramers doublets gives an additional contribution to the heat capacity under magnetic fields. The GSD g-factors g|| and g⊥ was estimated as 3.4 and 2.2, respectively, and Hex as 9 T.